Inflammation, in excess, was believed to be an underlying factor in the pathogenesis of proliferative cardiovascular diseases such as atherosclerosis. Phospholipase A2s (PLA2s) play an important role in inflammation. Arachidonic acid (AA), which is produced primarily by PLA2s, metabolizes via the cyclooxygenase (COX), lipoxygenase (LOX) and cytochrome P450 monooxygenase (CYP) pathways producing prostaglandins (PGs), hydroperoxyeicosatetraenoic acids (HPETEs) and epoxyeicosatrienoic acids (EETs), respectively. While some of the COX and LOX products of AA are proinflammatory, CYP, particularly CYP2C8/9 products of AA, are anti-inflammatory. Atherosclerotic arteries produce 15(S)-HETE as a major 15- LOX product of AA. Although the involvement of 15-LOX1 in the oxidation of low-density lipoprotein has been extensively studied in understanding its role in the pathobiology of atherosclerosis, very little is known in regard to its AA product, 15(S)-HETE, in atherosclerosis. In this regard, during the previous funding cycle of this grant application we have shown that 15(S)-HETE via inducing the expression of fibroblast growth factor-2, vascular endothelial growth factor and matrix metalloproteinase-2 modulates angiogenesis, an important factor in vascular wall diseases. During the course of these studies, we have discovered that 15(S)-HETE disrupts endothelial cell (EC) barrier function. Since one of the crucial functions of ECs is to maintain vessel wall integrity, perturbation in EC barrier function could be an initiation point for EC dysfunction and inflammation, two fundamental events in the pathogenesis of atherosclerosis. Based on these novel observations, we predict that eicosanoids, particularly the 15-LOX product of AA, namely, 15(S)-HETE via its capacity to perturb EC barrier function promotes paracellular movement of inflammatory cells into sub-endothelial space and sets the soil for the development of atherosclerosis. To address this hypothesis, we have proposed to test the following specific aims: 1. 15-LOX1-15(S)-HETE axis via tyrosine phosphorylation of tight junction (TJ) proteins disrupts TJs and thereby perturbs EC barrier function; 2. Non-receptor tyrosine kinases, Src and Pyk2 mediate 15- LOX1-15(S)-HETE-induced tyrosine phosphorylation of TJ proteins and their disassembly from TJs resulting in EC barrier dysfunction; 3. Mitogen-activated protein kinases (MAPKs) mediate 15-LOX1-15(S)-HETE-induced TJ protein serine/threonine phosphorylation and their disassembly from TJs resulting in EC barrier dysfunction and 4. 15-LOX1-15(S)-HETE axis via disrupting endothelial barrier function facilitates paracellular movement of inflammatory cells into the subendothelial space and promotes inflammation and atherosclerosis in response to feeding mice with high-fat diet. Thus, the experiments proposed in this grant application will provide novel information on the potential role of 15-LOX1-15(S)-HETE axis in endothelial barrier dysfunction leading to inflammation and atherosclerosis, which could be useful in the development of therapeutic drugs.